Electronic loose plate detector for printing press



W. H- STONE Sept. 8, 1 959 ELECTRONIC LOOSE PLATE DETECTOR FOR PRINTINGPRESS INVENTOR.

By ?/ZMM 9420M ATTORNEYS.

Filed July 20, 1956 ELECTRONIC LOOSE PLATE DETECTOR FOR PRINTING PRESSWilfred H. Stone, Des Moines, Iowa, assignor to Meredith PElblISIlillgCompany, Des Moines, Iowa, a corporation Iowa Application July 20, 1956,Serial No. 599,240

Claims. (Cl. 101-378) This invention relates to improvements in printingpresses and more particularly to improved means for detecting failuresin printing plates of the type utilized in high speed rotary printingpresses and the like.

Rotary printing presses, as well as operating personnel, are subject toinjury due to the failure of the printing plates utilized therewith. Onecause of such failure is. cracking of the plates during operation of theprinting press with the result that the plates are released from thehooks serving to clamp the plates to the press cylinders and are thrownoutwardly therefrom.

Printing plate failure also may be due to the continuous on and on"pressure applied to an electrotype plate during the printing operationas such pressure may cause the clamping hooks to shear through the leadbase of the plate and allow it to be thrown by centrifugal force fromthe cylinder.

Due to the existing dangers of such plate failures some form ofprotection for both the operating personnel and the printing press mustbe provided. Several schemes are known in the prior art for stopping theoperation of the printing press in the event of plate failure. However,these schemes generally are of a mechanical nature, and, due to theliabilities of mass and energy inherent in mechanical systems, they haveproved to be relatively slow acting. Accordingly, in such schemes it ispossible that the press may be stopped only after the press or itsoperating personnel have been damaged or injured. Manifestly such priorart schemes are not entirely satisfactory for use with the high speedrotary presses utilized in modern printing installations.

Accordingly, it is a general object of this invention to provide animproved loose plate detector for use with a printing press which isadapted to detect plate failure while the plate is still on the presscylinder and stop the operation of the printing press prior to thedefective condition reaching a stage of danger with regard to the safetyof the press and its operating personnel.

It is another object of this invention to provide such an improved looseplate detector which is electronic in nature and therefore is adaptableas a safety device for high speed printing presses.

It is still another object of this invention to provide an improvedloose plate detector for a printing press characterized by its highspeed of operation, its efficiency and its relative simplicity.

In accordance with features of a specific illustrative embodiment ofthis invention the loose plate detector comprises a gaseous dischargedevice which is maintained in a normally nonconducting condition by asuitable negative bias potential applied between its cathode and itscontrol grid. A relay is provided in the anode circuit of the dischargedevice and is adapted upon discharge of the latter to cause the printingpress to be shut down so that its defective condition may be remedied.It is a feature of this invention that the use of electronic detectionmeans enables a plate becoming loose on the press cylinder to bedetected and the press stopped before damage can occur.

The cathode of the discharge device is connected to a pluralty ofmetallic probes disposed in an insulated metallic mounting bar extendingover the press cylinder. In accordance with one embodiment of thisinvention the mounting bar is spaced approximately two inches from thecylinder and the metallic probes protruding from the bar are spacedwithin .010 inch from the plates so as to come into contact therewithwhen the plate becomes loose. In the event of such contact the biasingpotential is removed from the discharge device and the latter conductsto shut down the printing press. It is a further feature that shut downof the printing press also de-energizes the electronic portions of thedetector so that the latter is reset and in condition for further oper-.ation when the press is repaired and is caused to run once again.

The above and other features of novelty which characterize the inventionare pointed out with particularity in the claims appended to and forminga part of this specification. For a better understanding of thisinvention, its advantages and specific objects attained by its usereference is had to the accompanying drawing and descriptive material inwhich is shown and described an illustrative embodiment of theinvention.

In the drawing:

Figure 1 is a perspective view of one embodiment of the press cylinder,printing plate and probe mount construction in accordance with theinvention;

Figure 2 is a cross section of a mounted line 2-2 of Figure 1;

Figure 3 is a cross section of the mounting and insulating bars taken online 33 of Figure 1; and

Figure 4 is a schematic representation of the electronic control circuitembodying the invention.

Referring now to the drawing and particularly Figures 1, 2 and 3, thereis shown a specific illustrative embodiment of the sensing probemounting apparatus of the invention as utilized with a cylinder of arotary printing press. Although the invention is shown with a printingpress cylinder of the type having four plates mounted thereon it will beunderstood by those skilled in the art that the invention equally isapplicable to rotary printing presses having any desired number ofprinting plates.

Press cylinder 11 is supported by frame 13 of the printing press in sucha manner as to be freely rotatable therein when rotary driving power isapplied to shaft 15 of the cylinder. Many devices for rotating cylinder11 are known and it will be understood by those skilled in the art thatany of these devices suitable for the purpose of driving cylinder 11 maybe utilized therewith. In accordance with a preferred embodiment of theinvention, however, cylinder 11 is driven by means of an electric motorconnected to shaft 15 through suitable transmission means.

A plurality of arcuate printing plates such as plates 17, 19, 21 and 23,are secured to the surface of cylinder 11 by suitable clamping meanssuch as books and the like. A plurality of probes of conductive materialare supported in spaced relation from the plates by means of anelongated mounting bar 25 disposed substantially parallel to the axis ofrotation of cylinder 11. Thus, mounting bar 25 supports probe 27 aboveplate 17, probe 29 above plate 19, probe 31 above plate 21, and probe 33above plate 23. Mounting bar 25 is supported by means of an insulatingbar 35 which advantageously may be formed of rubber, plastic or thelike, secured to the press frame 13. Each probe is adapted by means of athreaded insert 37 and a nut 39 to be positioned a desired amount abovethe surface of its associated printing plate.

As shown in greater detail in Figure 2, each probe, as for example probe29, is inserted through a bore provided Patented Sept. 8, 1959' probetaken on probe'is spaced avdesired amount from the surface of theprinting plate 19; A threaded nut 39, which also is tapered at its innersurface to accommodateferrule 41, is.screwed on insert 37 to increasethe clamping pressure of ferrule 41 on probe 29 to maintain the probe ina fixed manner at the desired position.

Thus it will be appreciated that there is a highly conductive electricalpathfrom tip 43 of the probe throughv insert 37 and mounting bar 25. Inthe absence of a defective'printing'plate there is no electrical pathbetween the press frame 13 and the probes, since, as shown in Figure 3,mounting bar 25 is supportedby means of an insulating bar 35 disposedbetween press frame 13 and the mounting bar. Advantageously this isbrought about by means of a stud 45 inserted through mounting bar 25 andinsulating bar 35 and threaded into press frame 13. Electricalinsulation is provided by a layer of insulating material 47 completelysurrounding stud 45 so as to be disposed between the stud and theadjacent portions of mounting bar 25.

Referring now to Figure 4, the electronic control circuit there showncomprises a gaseous discharge device 10 which advantageously may be ofthe type generally known as a thyratron and which comprises a heaterfilament 12, a cathode 14, a control grid'lo, a screen grid:18 and ananode 20. In the operation of the invention discharge device 10 normallyis maintained in its nonconducting condition by a biasing potentialapplied between control grid 16 and cathode 14 and is placed in itsconducting condition by the removal of this biasing potential due to aprinting plate becoming loose on the press cylinder and contacting oneor more of plates 17, 19, 21 and 23.

Operating potentials are supplied to the discharge device 10 by a fullwave rectifier circuit which comprises a power transformer 22 having aprimary winding 24 con nected through a power switch 26 and a currentlimiting fuse 28 to a source of A.C. voltage 30. One secondary winding32 of power transformer 22 has its windings connected to heater filament12 of discharge device 10 and supplies heater current thereto.

Secondary winding 34 of power transformer 22 has one terminal thereofconnected to anode 36 and the other terminal thereof connected to anode38 of a full wave rectifier tube 40. Secondary winding 34 has aconductor 42 which is connected to a center tap thereon and alsoadvantageously is connected to ground. Heater filament 44 of rectifiertube 40 is connected to the terminals of heater winding 32 oftransformer 22.

Cathode 46 of rectifier 40 is connected to a filter network whichcomprises a pair of condensers 48 and t! connected across the rectifiertube output and a filter choke 52 connected in series with the tubecathode and between condensers 48and 50 in network fashion.

A-voltage dividing resistance network comprising resistances 54 and 56-is connected across the rectifier output'at condenser 50. Anode 20 ofgaseous discharge is connected through the windings of a relay 58 to therectifier output at the junction of choke 52 and condenser 50% Inaccordance with one specific embodiment of the invention the rectifieroutput at this point may have a potential of approximately 200 volts.Cathode 14 of gaseous discharge 10 is connected to the junction ofresistances 54 and 56. In accordance Wit-hsaid specific embodiment theseresistances are chosen such that the output potential at their junctionis approximately 30 volts. Cathode 14 also is connected to screen grid18 of dischargedevice 10.

Control grid 16 of discharge device 10 is connected to ground. Thus, itwill be appreciated that when the circuit is inthe condition shown inthe drawing there is a negativebiasing potential of 30. volts betweencontrol grid 16 and cathode 14 of discharge device 10. This potentialserves to maintain discharge device 10 in its nonconducting condition inthe normal operation of the detector control circuit.

Cathode 14 of discharge device 10 also is connected to a plurality ofmetallic probes such as probes 27 and 29 supported by mounting bar 25above press cylinder 11 in the manner described above. In accordancewith the specific embodiment of the invention mounting bar 25 ispositioned approximately two inches above the surface of the arcuateprinting plates, such as 17 and 19, secured to thesurface of presscylinder 11: In this embodiment sensing. probes 27 and 29 were set intobar 25 so as to protrude therethrough to Within .010 of an inch of thesurface of the printing plates. Press cylinder 11 is connected by meansof conductor 70 to ground.

It now is clear that if, during the operation of the printing'press, aplate becomesaloose and moves as little as .010 of an inch so as to comeinto contact with a sensing probe a circuit will be completed betweencathode 14 of discharge device 10 and ground through the probe, theloose printingplate, press cylinder 25 and conductor 70. This actionresults inthe removal of the negative biasing potential from dischargedevice 10 and the latter is'triggered to conduction. Relay 58 in theanode circuit of discharge device It) thereupon is energized to closeits contacts 72'and '74. This causes latching relay '78 to be energizedby battery to open its contacts 82 and 84 and break the circuit betweenA0. source 86 and press cylinder motor 88. Consequently, the printingpress is shut down to permit repair or replacement of thede= fectiveplate.

Advantageously, a pilot light 76 is connected'in series with contacts 72and 74 of relay 58, battery 80 and relay 78 to indicate by its lightedcondition the operation'of the detector circuit. This signals theprinting press personnel to investigate for a loose plate condition asthe cause of the press shut down.

Advantageously, power switch 26 is operatively asso-' ciated withlatching relay 78 and is opened by the opera-;

tion of the latter to de-energize the detector circuit and resetdischarge device 10. When the'defective condition of the press isremedied the operator presses the reset button the latching relay tostart the press cylinder motor 88-and to close power switch 26 of thedetector circuit for further operation.

It will be understood by those skilled in the art that modifications maybe made in the construction and ar rangement of the parts of the abovedescribed loose plate detector without departing from the real spiritand purpose of the invention and that it is intended to cover' by theappended claims any modified forms of struc tures or use of equivalentswhich reasonably may be included within their scope.

What is claimed is:

1. Means for detecting a defective plate on a printing press comprisingthe combination of a printing press cylinder, drive means for causingsaid cylinder to rotate, a press plate adapted to be secured to saidcylinder, sens ing means associated with said press plate and held inclosely spaced relation therewith, electronic circuit means connected tosaid sensing means and said cylinder adapted to be operated wheneversaid press plate becomes loose on said cylinder and comes intoelectrical contact with said sensing means, said electronic circuitmeans including a discharge device, a source of potential, means for' tothe energization of said relay means for stopping said drive means toterminate rotation of said cylinder and,

circuit means responsive to the press plate coming into electricalcontact with said sensing means for removing the cut-ofi bias from saiddischarge device and causing the latter to conduct to energize saidrelay means.

2. The combination of a printing press cylinder, means for causing saidcylinder to rotate, a plurality of press plates adapted to be secured tosaid cylinder, sensing means associated with said press plates and heldclosely spaced therefrom, electronic circuit means including a dischargedevice, means for applying a cut-ofi potential to said discharge deviceto maintain the latter in a normally nonconducting condition, meansconnected in circuit with said discharge device adapted to be energizedonly upon conduction of the latter for shutting off said drive means,and circuit means responsive to said sensing means being placed intoelectrical contact with any one of said plurality of press plates as aresult of said press plates becoming loose on said cylinder for removingthe cut-ofi potential from said discharge device and causing the latterto conduct.

3. Apparatus for detecting a loose plate on a printing press comprisingin combination a printing press cylinder, drive means for causing saidcylinder to rotate said drive means including an electric motor andswitch means for applying operating potentials to said motor, aplurality of plates adapted to be secured to said cylinder, sensingprobe means associated with said plates and held closely spacedtherefrom, electronic means including a discharge device connected tosaid sensing probe means, said discharge device being normallynonconductive and adapted to be rendered conductive whenever a platebecomes loose on said cylinder and comes into electrical contact withsaid sensing probe means, and means connected in circuit with saiddischarge device adapted to be energized only upon conduction of thelatter to open said switch means to stop rotation of said motor and saidcylinder.

4. Apparatus for stopping the rotation of a printing press cylinder uponthe detection of a defective plate thereon comprising an elongatedsupport member positioned above the cylinder in parallel with its axis,said support member being formed of a conductive material, at least oneconductive finger disposed in said support member and maintained inclosely spaced relation to said plate, a discharge device including ananode, a cathode and a control grid, means for applying a cut-01fpotential between said control grid and said cathode to maintain saiddischarge device in a normally nonconducting condition, means forconnecting said cylinder to said control grid, means for connecting saidcathode to said finger whereby any contact between a defective plate andsaid finger causes said cut-off potential to be removed from saiddischarge device to enable it to conduct, and actuating means connectedto said anode of said discharge device adapted to be energized inresponse to the conduction of the latter for stopping the rotation ofsaid press cylinder.

5. Apparatus for stopping the rotation of a printing press cylinder uponthe detection of a defective plate thereon comprising a cylinder drivemeans for rotating said cylinder, an elongated support member ofconductive material positioned above the cylinder in parallel with itsaxis of rotation, a bar of insulating material securing said support tothe printing press frame, at least one metallic finger disposed in saidsupport member and maintained closely spaced from said press plate, adischarge device including a pair of electrodes, means for applying acut-ofif potential to said pair of electrodes of said discharge deviceto maintain it in a normally nonconducting condition, means forconnecting said cylinder to said one of said electrodes, means forconnecting said metallic finger to the other of said electrodes wherebyany contact between a plate and said finger causes said cut-offpotential to be removed from said discharge device to enable saiddischarge device to conduct, and actuating means connected to saiddischarge device adapted to be energized in response to the conductionof the latter for de-energizing said drive means stopping the rotationof said press cylinder.

6. Safety apparatus for a printing press comprising a press cylinder,drive means for rotating said cylinder, an elongated support member ofconductive material positioned above the cylinder in parallel with itsaxis of rotation, a plurality of plates positioned on said cylinder, aplurality of metallic fingers disposed in said support member andmaintained in closely spaced relation to said plates, a dischargedevice, bias means for applying a cutoif potential to said dischargedevice to maintain it in a normally nonconducting condition, means forconnecting said discharge device to said cylinder and said fingers suchthat any contact of a plate with said fingers causes said cut-oft"potential to be removed from said discharge device to enable saiddischarge device to conduct, and actuating means connected to saiddischarge device adapted to be energized in response to the conductionof the latter for de-energizing said drive means and stopping therotation of said cylinder.

7. Safety apparatus for a printing press in accordance with claim 6wherein said drive means for rotating said cylinder comprises anelectric motor, and further comprising a source of power connected tosaid motor and a switch responsive to the operation of said actuatingmeans connected between said motor and said source of power wherebyenergization of said actuating means opens said switch to de-energizesaid electric motor.

8. Safety apparatus for a printing press in accordance with claim 7further comprising a second source of power, and a second switchconnected between said second source of power and said bias means, saidsecond switch being responsive to the energization of said actuatingmeans for opening the circuit between said second source of power andsaid bias means to de-energize the latter.

9. Safety apparatus for a printing press in accordance with claim 6further comprising an indicator in circuit with said actuating means andresponsive to the energization of the latter for signalling a defectiveplate condition.

10. Safety apparatus for stopping the rotation of a printing presscylinder upon the detection of a loose plate thereon comprising a pressframe, a press cylinder rotatably mounted in said frame, a plurality ofprinting plates on said cylinder, a support member of conductivematerial positioned adjacent the cylinder and in parallel with its axisof rotation, an insulating bar adapted for mounting said support memberto said frame, a plurality of sensing fingers in said support member andextending therethrough in closely spaced relation to said press plates,means for enabling the spacing between said fingers and said plates tobe adjusted as desired, a discharge device including an anode, a cathodeand a control grid, means for applying a cut-elf potential between saidcontrol grid and said cathode to maintain said discharge device in anormally nonconducting condition, means for connecting said cylinder tosaid control grid, means for connecting said cathode to said fingerswhereby any contact between a loose plate and said fingers causes saidcut-oil potential to be removed from said discharge device to enablesaid discharge device to conduct, and actuating means connected to saidanode of said discharge device adapted to be energized in response tothe conduction of the latter for stopping the rotation of said presscylinder.

References Cited in the file of this patent UNITED STATES PATENTS1,057,134 Evensen Mar. 25, 1913 1,257,833 Fankboner Feb. 26, 19181,257,834 Fankboner Feb. 26, 1918 1,340,355 Wood May 18, 1920 1,708,196Wood Apr. 9, 1929 1,856,162 Isbell May 3, 1932 2,200,316 Wieking May 14,1940 2,431,316 Dudley Nov. 25, 1947

